1. Field of the Invention
The present invention relates to a mobile communication system for performing standby control of mobile units for car telephones, portable telephones, etc.
Mobile units of various designs have been commercialized for mobile telephones such as car telephones and portable telephones, and an even wider variety of mobile units are expected to come into use in the future. For such a wide variety of mobile units, control must be performed to ensure the required communication quality.
2. Description of the Related Art
In a mobile communication system, standby control is performed to control whether a mobile unit is placed in a state (standby state) ready to receive service from a base station. For such standby control, standby control information containing data on a communication level and a communication out level is sent from the base station to each mobile unit to notify the mobile unit accordingly. The mobile unit that has received the standby control information reads the communication level and communication out level, and measures the reception level for comparison. When not in a standby state, if the reception level becomes greater than the communication level, the mobile unit goes into a standby state. Conversely, when in a standby state, if the reception level falls below the communication out level, the mobile unit goes out of the standby state.
In previous systems, the communication level and the communication out level have been set at respective fixed levels regardless of the performance of individual mobile units. However, with a mobile unit with improved reception performance by the use of a diversity reception technique, etc., a higher communication quality than is possible with an ordinary mobile unit not equipped with a diversity reception system can be obtained at the same reception level. The problem with previous systems has therefore been that a high-performance mobile unit does not enter a standby state even when the reception level is good enough to provide good communication quality for such a mobile unit, thus being unable to make full use of the high reception performance of the mobile unit.